Field of the Invention
The present invention relates to a bottom-supported fluidized bed boiler with a support construction for a particle separator. More particularly, the invention relates to a fluidized bed boiler comprising a bottom-supported furnace, at least one particle separator with a support construction in gas flow connection with an upper portion of the furnace and comprising a furnace side portion, an outer portion opposite to the furnace side portion and a conical lower portion, and at least two bottom-supported downcomer pipes in fluid connection with a steam drum and adjacent to the outer portion of the particle separator.
Description of Related Art
Fluidized bed boilers comprise a furnace for combusting fuel and at least one discharge channel connected to an upper portion of the furnace for discharging flue gas and solid particles from the furnace. Solid particles are generally separated from the flue gas in a particle separator so as to return at least a portion of the particles via a return channel to a lower portion of the furnace. The return channel is often provided with a heat exchange chamber for recovering heat from the separated particles.
Particle separators used in the fluidized bed boilers are generally cyclone separators having a cylindrical upper portion and a conical lower portion. According to a conventional construction, the cylindrical upper portion has a circular crosssection, but during the last two decades, polygonal cross sections, such as square or octagonal cross sections, have become more and more common. Correspondingly, the cross section of the conical lower portion can vary from circular to different polygonal shapes.
Relatively large fluidized bed boilers are generally arranged to be top-supported, i.e., so that the furnace and particle separator (or particle separators) are arranged to hang from a rigid supporting structure. Relatively small fluidized bed boilers may alternatively be arranged to be bottom-supported. The main difference between the top-supported and bottom-supported construction is that when the boiler heats up to its operating temperature, the thermal expansion of a top-supported boiler takes place mainly downwards, whereas in a bottom-supported boiler, the thermal expansion takes place mainly upwards. Bottom supported boilers are generally simpler and economically more advantageous than top-supported boilers, especially in the case of small fluidized bed boilers, because they do not require a separate supporting structure. A disadvantage of bottom-supported construction is that the walls have to be strong enough to carry the compression load of the structures above.
A special problem in bottom-supported fluidized bed boilers is the supporting of the particle separator. Because the bottom of the particle separator is generally at a higher level than the bottom of the furnace, the bottom of the particle separator is, according to a conventional solution, supported by a special support leg to the ground or founding of the boiler plant.
Published European Patent Document EP 760071 B1 discloses a bottom-supported circulating fluidized bed boiler comprising a steam drum on top of two bottom-supported downcomer pipes and a cooled rectangular cyclone separator having a common wall with the furnace and an opposite wall, or front wall, connected to the downcomer pipes. A disadvantage of this construction is that the common wall of the two units, i.e., of the furnace and the separator, has to be made especially strong to carry a large portion of the weights of both units.
Published International Patent Document WO 2007/135238 A2 discloses a top-supported circulating fluidized bed boiler comprising a particle separator hanging from a supporting structure by the aid of a frame connected to the upper portion of the separator.
An object of the present invention is to provide a bottom-supported fluidized bed boiler with a simple and a reliable means for supporting the particle separator.